A large number of applications and potential applications exist for imaging systems such as projection displays that are used to display information. Such applications include, but are not limited to, general indoor signage (e.g. shopping malls, arcades, etc.), transportation signage (e.g. arrival/departure times, etc.), in-lobby signage for office buildings, control rooms, restaurants signage, etc.
It is known to provide large displays for signage and the like by assembling a multiplicity of individual display units in an array (see, for example, United States Patent Publication No. 2008/0284675, the contents of which are incorporated herein by reference). The construction of each individual display unit is preferably similar and may include a chassis for housing projection lamps, electronic circuits, etc., and a rear projection screen.
A modular array of display units may be created by connecting or attaching together adjacent display unit chassis. The attachment system should be simple and reversible, in order to permit re-configuring the array in different shapes. For example, in order to simplify the construction and deconstruction of the array it may be advantageous to provide an attachment system that is accessible from the top of each display unit chassis. For example, a long screw may be inserted into the top of a first display unit chassis so as to extend through the chassis and protrude from the bottom for insertion into a complementary female thread of a further display unit on which the first display unit is stacked. However, if the units are of identical construction a difficulty arises since the screw from the first (upper) display unit will be coincident with the screw used to connect the second (lower) display unit to any additional display unit on which it is stacked.